An international panel of aviation experts indicates that U.S. regulatory authorities failed to adequately investigate and certify the anti-stall technology used in Boeing 737 MAX airliners, which remain grounded following two deadly plane crashes over the last year.

On October 11, the Federal Aviation Administration (FAA) received a Joint Authorities Technical Review (JATR) (PDF) on the 737 MAX’s flight control system, which was put together by technical representatives and civil experts from the FAA, the National Aeronautics and Space Administration (NASA), Australia, Brazil, Canada, China, Europe, Indonesia, Japan, Singapore, and the United Ara Emirates.

According to the findings, the FAA dropped the ball on the certification process for the anti-stall system used in the Boeing planes, and the JATR is urging the FAA to review that process and has put forward an extensive list of recommendations.

The investigation was commissioned following two Boeing 737 Max plane crashes that occurred over the past year, each involving new aircraft that seemingly fell out of the sky shortly after take off.

The first Boeing 737 accident occurred on October 29, 2018, when Lion Air Flight 610 went down after departing from Jakarta, Indonesia airport, killing all 189 passengers and crew. Investigators determined that the pilots struggled for 11 minutes to keep the plane in the air, likely due to a problem with the plane’s Angle of Attack sensor, which kept telling an automated system that the pilots were unable to shut off that the nose should be pointed down.

A second crash occurred when another Boeing 737 Max plane crashed just minutes into its flight on March 10, 2019, killing all 157 passengers and crew on board Ethiopian Airline Flight 302. Shortly after this incident, the entire 737 Max fleet was grounded worldwide.

Both crashes were initially attributed to the aircrafts’ angle of attack system, which is the attitude of the wings in relation to airflow. When air flows over the wings at the correct angle, you get lift, which is what makes a plane fly. If the air is not flowing over the wings properly, the plane can stall, which occurs when it loses lift and begins to fall out of the sky.

“The FAA’s aircraft certification process has played a major role in producing airliners with an exemplary safety record consisting of a five-year worldwide average of only one fatal airliner crash for every 2 1/2 to 3 million flights, and a U.S. record of only one airline passenger fatality in more than 10 years,” the JATR findings note. “Nonetheless, as with any system that is designed and operated by humans, the certification process can never be perfect, and the two tragic crashes that resulted in the creation of the JATR reveal a critical need to review the process to determine whether improvement and modernization are warranted.”

At issue was the 737 MAX’s Maneuvering Characteristics Augmentation System (MCAS), which is part of the flight control computer and is designed to help prevent stalls, as well as the training of flight personnel on the use of the plane’s systems.

The JATR makes a host of both broad and specific recommendations. In one case, the team found that the MCAS was not evaluated as a complete and integrated system in the certification documents submitted to the FAA by Boeing. The FAA failed to adequately review, update or validate design assumptions made about the MCAS as well, resulting in both Boeing and the FAA missing key weaknesses in the system.

“The JATR team found that the MCAS was not evaluated as a complete and integrated function in the certification documents that were submitted to the FAA. The lack of a unified top-down development and evaluation of the system function and its safety analyses, combined with the extensive and fragmented documentation, made it difficult to assess whether compliance was fully demonstrated,” the report states. “The MCAS design was based on data, architecture, and assumptions that were reused from a previous aircraft configuration without sufficient detailed aircraft-level evaluation of the appropriateness of such reuse, and without additional safety margins and features to address conditions, omissions, or errors not foreseen in the analyses.”

The JATR also calls on the FAA to review whether Boeing’s Aviation Safety Oversight Office (BASOO) has adequate staff; ensure whether manufacturers are using industry best practices; require a documented process to determine what information will be in the flight manual, and should review training programs to ensure flight crews know what to do in the case of a stall event.

FAA Administrator Steve Dickson issued a statement on October 11, saying he will review every recommendation and take appropriate action.

“We welcome this scrutiny and are confident that our openness to these efforts will further bolster aviation safety worldwide,” Dickson said. “The accidents in Indonesia and Ethiopia are a somber reminder that the FAA and our international regulatory partners must strive to constantly strengthen aviation safety.”

The U.S. Department of Transportation and the Federal Bureau of Investigation have launched a criminal probe into the certification of the Boeing 737 MAX jet, in addition to ongoing investigations by the National Transportation Safety Board as well as French investigators.

Boeing has also promised to pay $144,500 to the families of every victim of the two accidents from a $100 million compensation fund. Those who lost loved ones in the accidents have until December 31, 2019 to participate in the compensation fund. However, filing a claim with the fund does not negate their ability to pursue an individual lawsuit against Boeing.

Boeing still faces more than 50 additional lawsuits linked to both crashes in the U.S. District Court for the Northern District of Illinois. The 737 MAX aircraft remains grounded worldwide.